Equisetum

Equisetum is a genus of ferns commonly known as the ‘horsetails’. They consist of 15 species of considerably unique plants from the class of ferns known as Equisetopsida.

Horsetails have a distinct growth form and spores with the ability to travel along the ground. They are found through most parts of Earth in wet environments.

Growth form

Horsetails have a unique growth form that distinguishes them amongst all other ferns. Their stems, leaves and roots are all quite unique and makes the Equisetum species a very interesting group of plants.

Their stems often appear to be formed by the combination of multiple smaller segments and they often resemble the stems of rushes. Stems grow either as straight erect stalks or creeping along the ground; they are hollow and reinforced with silica. The silica makes the stems of horsetails strong and hardened.

Equisetum leaves grow in whorls with multiple leaves growing from the same point around the stem and their branches also grow in the same fashion. Some species have tiny scale-like leaves and often appear leafless, whilst other species have long, slender leaves and give the plant a feathery appearance. The particular points where leaves sprout from are called nodes and the bases of their leaves are fused around the stem creating a collar.

Horsetail leaves are unusual because they only a single vein. A trait that they share with lycophytes, however the single vein in the Equisetum leaves is not believed to be an ancestral trait but rather evolved more recently.

Equisetum species have rhizomes that grow deep below the grounds surface. Some species have cone-like structures called strobili that produce and house the plants spores for reproduction. The tallest species can reach heights of more than 8 m but the majority of species do not grow taller than 2 m.

Distribution of equisetum

Horsetails enjoy wet environments and some species are even considered semi-aquatic. They are found in all continents except Antarctica and Australia and are also absent from the islands of the South Pacific such as Samoa, Fiji and New Zealand.

Diversity and taxonomy

There is a total of 15 species in the genus Equisetum although many of these species often hybridize with one another. Being ferns, Equisetum belong to the division Pteridophyta. They form their own class of ferns known as Equisetopsida and family Equisetaceae.

Reproduction of equisetum ferns

Horsetails reproduce using spores rather than seeds. Male and female spores are very similar and are stored in sporangia. Some species store their spores in cone-like structures called strobili.

Equisetum spores have elaters which help to spring spores out of their sporangia once it has split open. The elaters improve the dispersal of spores to new areas by allowing them to get higher and catch more wind. Elaters also enable Equisetum spores to travel along the ground.

Last edited: 23 May 2015

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